1. Field of the Invention
The present invention relates to a hybrid relay having
an electromagnetic relay system which includes at least one coil, a core yoke unit which passes through the coil, at least one armature, at least one contact pair which is switched by the armature, and PA1 a power semiconductor whose switching path, together with the at least one contact pair, switches the load circuit of the relay and whose switching time can be controlled to be offset in time with respect to that of the electromagnetic relay system wherein the contact pair is in each case switched on no-load.
2. Description of the Prior Art
When relay contacts are switched on load, they are severely stressed, primarily by the switching arc that occurs, and the large amount of heat produced can lead to welding of the contacts, or at least to undesirable material migration, to erosion and thus to a reduction in life. In order to avoid these effects, so-called hybrid relays are used which, in the manner stated initially, use an electronic switch in addition to the mechanical relay contacts. This electronic switch is operated offset in time and thus absorbs the load peaks during switching on and off; the relay contacts are in this case switched "dry" and, in consequence, can achieve a long life at low cost. Such hybrid circuits have been disclosed, for example, in DE 37 01 838 A1 or U.S. Pat. No. 4,772,809. Depending on the circumstances, relay contacts are connected either in parallel or in series with the power semiconductor in these circuits. In the former case, the power semiconductor is first switched on and then the relay contact is closed so that, in continuous operation, the load flows via the relay contact while the semiconductor need then carry only a relatively small proportion of the current or can be switched off entirely. The sequence during switching off is the reverse of this. In the second case, that is to say in the case of the series circuit, the relay contact is first closed and then the power semiconductor is switched on or, during switching off, the power semiconductor is switched off before the contacts are opened, with no current flowing through them. In this second case, the load current also flows continuously via the power semiconductor so that it also has to cope with a considerable heat loss. This series circuit is significant, for example, if two circuits have to be closed or opened precisely at the same time on a double relay or a polarity reversal relay.
In the case of conventional hybrid relays and hybrid circuits, conventionally designed electromagnet systems and standard semiconductors are connected using a conventional circuit technique. As a rule, this means that the two systems are arranged on a common printed circuit board, with a corresponding space requirement. In this case, the heat losses from the semiconductor also have to be dissipated in a conventional manner via heat sinks.
An object of the present invention, therefore, is to provide a hybrid relay of the type mentioned initially which has a compact design and which also allows good and simple heat dissipation for the power semiconductor while using as few individual parts as possible.